Fix FolderNameEditor memory leak on cancel (#769)

* Cleanup FolderNameEditor

* Match FolderBrowserDialog code in FolderNameEditor

Fix leaks

* PR feedback, more cleanup and fixes

* PR feedback

src/Common/src/Interop/Interop.HRESULT.cs

@@ -0,0 +1,11 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+internal static partial class Interop
+{
+    public static class HRESULT
+    {
+        public const int S_OK = 0;
+    }
+}

src/Common/src/Interop/Interop.Libraries.cs

@@ -0,0 +1,14 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+internal static partial class Interop
+{
+    public static partial class Libraries
+    {
+        internal const string Kernel32 = "kernel32.dll";
+        internal const string Gdi32 = "gdi32.dll";
+        internal const string User32 = "user32.dll";
+        internal const string Shell32 = "shell32.dll";
+    }
+}

src/Common/src/Interop/Kernel32/Interop.MAX_PATH.cs

@@ -0,0 +1,11 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+internal partial class Interop
+{
+    internal partial class Kernel32
+    {
+        internal const int MAX_PATH = 260;
+    }
+}

src/Common/src/Interop/Kernel32/Interop.MAX_UNICODESTRING_LEN.cs

@@ -0,0 +1,11 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+internal partial class Interop
+{
+    internal partial class Kernel32
+    {
+        internal const int MAX_UNICODESTRING_LEN = short.MaxValue;
+    }
+}

src/Common/src/Interop/Shell32/Interop.SHBrowseForFolder.cs

@@ -0,0 +1,53 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Diagnostics.CodeAnalysis;
+using System.Runtime.InteropServices;
+using Microsoft.Win32.SafeHandles;
+
+internal static partial class Interop
+{
+    public static partial class Shell32
+    {
+        [DllImport(Libraries.Shell32)]
+        public static extern CoTaskMemSafeHandle SHBrowseForFolderW(ref BROWSEINFO lpbi);
+
+        public delegate int BrowseCallbackProc(IntPtr hwnd, int msg, IntPtr lParam, IntPtr lpData);
+
+        public static class BrowseInfoFlags
+        {
+            public const uint BIF_RETURNONLYFSDIRS = 0x00000001;
+            public const uint BIF_DONTGOBELOWDOMAIN = 0x00000002;
+            public const uint BIF_RETURNFSANCESTORS = 0x00000008;
+            public const uint BIF_EDITBOX = 0x00000010;
+            public const uint BIF_NEWDIALOGSTYLE = 0x00000040;
+            public const uint BIF_NONEWFOLDERBUTTON = 0x00000200;
+
+            public const uint BIF_BROWSEFORCOMPUTER = 0x00001000;
+            public const uint BIF_BROWSEFORPRINTER = 0x00002000;
+            public const uint BIF_BROWSEFOREVERYTHING = 0x00004000;
+        }
+
+        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
+        public unsafe struct BROWSEINFO
+        {
+            public IntPtr hwndOwner;
+
+            public CoTaskMemSafeHandle pidlRoot;
+
+            public char *pszDisplayName;
+
+            public string lpszTitle;
+
+            public uint ulFlags;
+
+            public BrowseCallbackProc lpfn;
+
+            public IntPtr lParam;
+
+            public int iImage;
+        }
+    }
+}

src/Common/src/Interop/Shell32/Interop.SHGetKnownFolderPath.cs

@@ -0,0 +1,15 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Runtime.InteropServices;
+
+internal static partial class Interop
+{
+    public static partial class Shell32
+    {
+        [DllImport(Libraries.Shell32, CharSet = CharSet.Unicode, SetLastError = false, BestFitMapping = false, ExactSpelling = true)]
+        public static extern int SHGetKnownFolderPath(ref Guid rfid, uint dwFlags, IntPtr hToken, out string pszPath);
+    }
+}

src/Common/src/Interop/Shell32/Interop.SHGetPathFromIDListLongPath.cs

@@ -0,0 +1,79 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Diagnostics.CodeAnalysis;
+using System.Runtime.InteropServices;
+using Microsoft.Win32.SafeHandles;
+
+internal static partial class Interop
+{
+    public static partial class Shell32
+    {
+        [DllImport(ExternDll.Shell32, EntryPoint = "SHGetPathFromIDListEx", ExactSpelling = true)]
+        private static extern bool SHGetPathFromIDListEx(IntPtr pidl, IntPtr pszPath, int cchPath, int flags);
+
+        public static bool SHGetPathFromIDListLongPath(IntPtr pidl, out string path)
+        {
+            IntPtr pszPath = Marshal.AllocHGlobal((Interop.Kernel32.MAX_PATH + 1) * sizeof(char));
+            int length = Interop.Kernel32.MAX_PATH;
+            try
+            {
+                if (!SHGetPathFromIDListLongPath(pidl, ref pszPath, length))
+                {
+                    path = null;
+                    return false;
+                }
+
+                path = Marshal.PtrToStringAuto(pszPath);
+                return true;
+            }
+            finally
+            {
+                Marshal.FreeHGlobal(pszPath);
+            }
+        }
+
+        public unsafe static bool SHGetPathFromIDListLongPath(IntPtr pidl, ref IntPtr pszPath, int length)
+        {
+            // SHGetPathFromIDListEx is basically a helper to get IShellFolder.DisplayNameOf() with some
+            // extra functionally built in if the various flags are set.
+
+            // SHGetPathFromIDListEx copies into the ouput buffer using StringCchCopyW, which truncates
+            // when there isn't enough space (with a terminating null) and fails. Long paths can be
+            // extracted by simply increasing the buffer size whenever the buffer is full.
+
+            // To get the equivalent functionality we could call SHBindToParent on the PIDL to get IShellFolder
+            // and then invoke IShellFolder.DisplayNameOf directly. This would avoid long path contortions as
+            // we could directly convert from STRRET, calling CoTaskMemFree manually. (Presuming the type is
+            // STRRET_WSTR, of course. Otherwise we can just fall back to StrRetToBufW and give up for > MAX_PATH.
+            // Presumption is that we shouldn't be getting back ANSI results, and if we are they are likely
+            // some very old component that won't have a > MAX_PATH string.)
+
+            // While we could avoid contortions and avoid intermediate buffers by invoking IShellFolder directly,
+            // it isn't without cost as we'd be initializing a COM wrapper (RCW) for IShellFolder. Presumably
+            // this is much less overhead then looping and copying to intermediate buffers before creating a string.
+            // Additionally, implementing this would allow us to short circuit the one caller (FolderBrowserDialog)
+            // who doesn't care about the path, but just wants to know that we have an IShellFolder.
+            while (SHGetPathFromIDListEx(pidl, pszPath, length, 0) == false)
+            {
+                if (length >= Kernel32.MAX_UNICODESTRING_LEN
+                    || *(char*)pszPath.ToPointer() == '\0')
+                {
+                    // Already at the maximum size string, or no data was copied in. Fail.
+                    return false;
+                }
+
+                // Try giving the API a larger buffer
+                length = length * 2;
+                if (length > Kernel32.MAX_UNICODESTRING_LEN)
+                    length = Kernel32.MAX_UNICODESTRING_LEN;
+
+                pszPath = Marshal.ReAllocHGlobal(pszPath, (IntPtr)(length * sizeof(char)));
+            }
+
+            return true;
+        }
+    }
+}

src/Common/src/Interop/Shell32/Interop.SHGetSpecialFolderLocation.cs

@@ -0,0 +1,16 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Runtime.InteropServices;
+using Microsoft.Win32.SafeHandles;
+
+internal static partial class Interop
+{
+    public static partial class Shell32
+    {
+        [DllImport(Libraries.Shell32, EntryPoint = "SHGetSpecialFolderLocation", ExactSpelling = true)]
+        public static extern int SHGetSpecialFolderLocation(IntPtr hwnd, int csidl, out CoTaskMemSafeHandle ppidl);
+    }
+}

src/Common/src/Microsoft/Win32/SafeHandles/CoTaskMemSafeHandle.cs

@@ -0,0 +1,25 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Runtime.InteropServices;
+
+namespace Microsoft.Win32.SafeHandles
+{
+    internal sealed class CoTaskMemSafeHandle : SafeHandle
+    {
+        internal CoTaskMemSafeHandle() : base(IntPtr.Zero, true)
+        {
+        }
+
+        public override bool IsInvalid => IsClosed || handle == IntPtr.Zero;
+
+        protected override bool ReleaseHandle()
+        {
+            Marshal.FreeCoTaskMem(handle);
+            handle = IntPtr.Zero;
+            return true;
+        }
+    }
+}

src/Common/src/NativeMethods.cs

@@ -361,27 +361,7 @@ public const int
         CONNECT_E_NOCONNECTION = unchecked((int)0x80040200),
         CONNECT_E_CANNOTCONNECT = unchecked((int)0x80040202),
         CTRLINFO_EATS_RETURN    = 1,
-        CTRLINFO_EATS_ESCAPE    = 2,
-        CSIDL_DESKTOP                    = 0x0000,        // <desktop>
-        CSIDL_INTERNET                   = 0x0001,        // Internet Explorer (icon on desktop)
-        CSIDL_PROGRAMS                   = 0x0002,        // Start Menu\Programs
-        CSIDL_PERSONAL                   = 0x0005,        // My Documents
-        CSIDL_FAVORITES                  = 0x0006,        // <user name>\Favorites
-        CSIDL_STARTUP                    = 0x0007,        // Start Menu\Programs\Startup
-        CSIDL_RECENT                     = 0x0008,        // <user name>\Recent
-        CSIDL_SENDTO                     = 0x0009,        // <user name>\SendTo
-        CSIDL_STARTMENU                  = 0x000b,        // <user name>\Start Menu
-        CSIDL_DESKTOPDIRECTORY           = 0x0010,        // <user name>\Desktop
-        CSIDL_TEMPLATES                  = 0x0015,
-        CSIDL_APPDATA                    = 0x001a,        // <user name>\Application Data
-        CSIDL_LOCAL_APPDATA              = 0x001c,        // <user name>\Local Settings\Applicaiton Data (non roaming)
-        CSIDL_INTERNET_CACHE             = 0x0020,
-        CSIDL_COOKIES                    = 0x0021,
-        CSIDL_HISTORY                    = 0x0022,
-        CSIDL_COMMON_APPDATA             = 0x0023,        // All Users\Application Data
-        CSIDL_SYSTEM                     = 0x0025,        // GetSystemDirectory()
-        CSIDL_PROGRAM_FILES              = 0x0026,        // C:\Program Files
-        CSIDL_PROGRAM_FILES_COMMON       = 0x002b;        // C:\Program Files\Common
+        CTRLINFO_EATS_ESCAPE    = 2;
 
         public const int DUPLICATE = 0x06,
         DISPID_UNKNOWN = (-1),
@@ -1007,8 +987,6 @@ public static int MAKELCID(int lgid, int sort) {
 
 
         public const int MEMBERID_NIL = (-1),
-        MAX_PATH = 260,
-        MAX_UNICODESTRING_LEN =  short.MaxValue, // maximum unicode string length 
         ERROR_INSUFFICIENT_BUFFER = 122, //https://msdn.microsoft.com/en-us/library/windows/desktop/ms681382(v=vs.85).aspx
         MA_ACTIVATE = 0x0001,
         MA_ACTIVATEANDEAT = 0x0002,
@@ -3270,9 +3248,9 @@ public class OPENFILENAME_I
             public int      nMaxCustFilter = 0;
             public int      nFilterIndex;
             public IntPtr   lpstrFile;
-            public int      nMaxFile = NativeMethods.MAX_PATH;
+            public int      nMaxFile = Interop.Kernel32.MAX_PATH;
             public IntPtr   lpstrFileTitle = IntPtr.Zero;
-            public int      nMaxFileTitle = NativeMethods.MAX_PATH;
+            public int      nMaxFileTitle = Interop.Kernel32.MAX_PATH;
             public string   lpstrInitialDir;
             public string   lpstrTitle;
             public int      Flags;